Trajection is set in motion along with the biosphere, in the worlds of the living. It is the passage from the abstraction of the Umgebung to the concrescence of the Umwelt. This contingent history surely begins with life but probably even before life, in the physical world, or even in mathematical laws. Concrete history where the number of bodies is virtually infinite, exponentially increases this uncertainty, before moderating it by the law of large numbers. It is not important to analyze the different mechanisms in themselves, but on the contrary to find their common principle – trajection as an evolutionary and historical principle. With life appears the interpreter that not only looks for what surrounds it but also gives it meaning. It not only perceives its surroundings, but also acts on them and thus reproduce their existence as its own milieu.